Aqueous dispersion of vinylidene chloride polymers containing hydrogen peroxide as acorrosion inhibitor



, 2,744,080 Patented May 1, I 1956 United States PatentiQflice I Gilbert W. Brant, deceased, late of Buffalo, N. Y., by

Bernice Brant Hankovich, administratrix,

Buifalo, N. Y.,

assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application September 24, 1951, Serial No. 248,104

2 Claims. 01. 260 29.6

No Drawing.

This invention relates to improvements in aqueous dispersions of vinylidene chloride polymers suitable for coating regenerated cellulose film, cellulose acetate film, linearpolyester film, etc. More particularly, this invention relates to improvements in such aqueous-dispersions whereby said dispersions are rendered substantially noncorrosive to metals, especially chromium, at elevated temperatures.

In coating continuous web or sheet base material such as regenerated cellulose film and the like, with aqueous dispersions of vinylidene chloride polymers, particularly c'opolymers', it has been proposed to pass the coatedweb over one or more polished metal rolls heated to a'temperature sufficient to drive off excess moisture from the freshly coated web. Because of the well known hardness and resistance to corrosion of chromium under oxidizing conditions, and because chromium ordinarily retains a high polish, it has further been proposed to use chromium plated rolls. It has been found, however, that at the usual drying temperatures, e. g., temperatures of about 100 C., aqueous dispersions of vinylidene chloride polymers corrode chromium plate to such an extent that the usefulness of chromium plated rolls for the purpose is seriously impaired. Corrosive action of the dispersions is evidently due to sodium chloride present as an impurity in the dispersing agent, a small amount of sulfuric and, perhaps, sulfurous acid from the, catalyst system employed in the polymerization reaction, and, presumably, hydrochloric acid liberated from the sodium chloride by the sulfuric acid. It iswell known that chromium is highly resistant to corrosion under oxidizing conditions but is readily attacked under reducing conditions. It is said that the metal exists in two states-passive and active, the former being the normal state when chromium is in contact with air. It is thought that chromium resists attack as long as it remains passive but loses its resistance when converted to the active state. It is activated and attacked by certain non-oxidizing acids such as sulfuric and hydrochloric and is activated, but not necessarily attacked, by certain ions, notably chloride ions. Thus, chromium resists attack by sodium chloride but loses its resistance to many other substances in the presence of sodium chloride. In the search for means to prevent or inhibit corrosion, it was found that neutralizing the dispersion acidity prevented corrosion but rendered the dispersion unstable. From this it appeared that to -be satisfactory, a corrosion inhibitor must prevent corrosion despite the presence of the activating and corrosive elements normally and necessarily present in a dispersion.

An object of this invention, therefore, is to prevent or inhibit the corrosion of metal surfaces, particularly chromium surfaces, when brought in contact with aqueous dispersions of vinylidene chloride polymers suitable as coating compositions for film, etc. Another object is to render such dispersions non-corrosive to chromium plate without impairing the stability of the dispersion or 2 otherwise deleteriously affecting the same. These and other objects will more clearly appear hereinafter.

I'have found that the presence of a small amount of hydrogen peroxide, H202, in the aqueous dispersion coat-- ing composition effectively inhibits the corrosive action of the dispersion. Accordingly, the above objects are realized by my invention which, briefly stated, comprises incorporating in dispersions of vinylidene chloride polymers containing impurities which render the dispersions corrosive to metals, from about 0.1% to about 1% by weight, based on the total weight of the dispersion,-of hydrogen peroxide.

The corrosion inhibitor of this invention is effective with aqueous dispersions of any polymer of vinylidene chloride, said dispersions containing an anionic com pound as the dispersing agent. Examples of representative vinylidene chloride polymers and aqueous dispersions thereof suitable for coating and susceptible of improvement in accordance with this invention, are disclosed in the copending application of Lewis & Meier, U. S. Serial No. 101,262, filed June 24, 1949, now abandoned.

The hydrogen peroxide should be incorporated in the aqueous dispersion in an amount within the range of from about 0.1% to about 1% by weight, based on the total weight of the dispersion. Concentrations of hydrogen peroxide below about-0.l% are insufiicient to prevent substantial corrosion of chromium plate, whereas not over 1% of hydrogen peroxide will be required to completely prevent corrosion in most instances. Preferably, from 0.4% to 0.6% hydrogen peroxide should be used for optimum results.

If desired, a sizing ingredient may be added to the dispersions to facilitate separating cut sheets of the coated material, or, the webs may be sized in a separate step after being coated.

The following examples further illustrate the practice and principles of this invention. Parts and percentages are by weight unless otherwise indicated.

Example I A dispersion was. prepared by adding 193 parts of vinylidene chloride and 107 parts of acrylonitrile to a mixture consisting of 700 parts of water, 15 parts of Darvan #1 (sodium beta naphthalene sulfonate condensed with formaldehyde), 3 parts of ammonium persulfate, and 1.5 parts of meta sodium bisulfite, and maintaining the resulting mixture at 33 to 34 C. under reflux and with stirring, to effect polymerization. To the copolymer dispersion so obtained was added, with stirring, 17 parts of 30% hydrogen peroxide in 8 parts of water; and this composition containing 0.5% hydrogen peroxide, based on the total weight of the dispersion, was dried on chromium plated panels at C. No corrosion of the panels occurred. The same dispersion with no hydrogen peroxidecorroded the chromium plate badly under the same drying conditions.

Example III A dispersion prepared from 141 parts of vinylidene chloride, 20 parts of acrylonitrile, 8 parts of itaconic acid, I

2,744, oao

400 parts of water, 8 parts "of Duponol ME (sodium salts .of .sulfated straight -chain alcohols ranging from Cm to Cm), 0.3 part of ammonium persulfate, and 0.15 part of meta sodium bisulfite, to which was added 11 parts of 30% hydrogen tperoxide in 5.5 parts of 'water (0.4% hydrogen peroxide :coneentration) 'was dried "on chromium plated panels at 100 C. with no corrosion.

Chromium plated 1 panels coated with 'the 'same dispersion but containing-no -"Hz0zrwere corroded 'at 100 C.

Example IV by'theabove dispersion fbut was corroded when anidentical dispersion was :tested containing no hydrogen peroxide .(0.45% hydrogen peroxide was used).

Example V A copolymer dispersion 'from 64 partst-of nvinylidene chloride, 16 parts of vinyl chloride, 120 :parts 10f water, 2.4 parts of Duponol ME, 0.4 'part of ammonium persulfate, and 0.2 ,part of meta :sodium bisulfite was prepared as in the precedingexamples; and .to thistdispersion was-added-4 parts of 30% hydrogen peroxide .in2 parts 30 of water (-0.6% .of H202 based .on the -weightcof1the :dis persion). The resulting dispersion did-not corrode "chromium at 100 C., whereas the same dispersion minus the hydrogen peroxide caused corrosion.

From the foregoing, it is apparent that hydrogen peroxide as a corrosion inhibitor in vinylidene chloride copolymer aqueous dispersion coating compositions is completely efiective at relatively low concentrations. Moreover, it does not impair the stability of the dispersion; and, ?because it is apparently removed from the scoating duringdrying, itdoes not impair coatingquality'withrcspect to toxicity, color, odor, taste or otherwise.

As many changes maybe made without-departing'fmm the 'scope and spirit :of my invention, it is to .be understood that .said invention is in no wise restricted except as set forth in the appended claims.

What :is claimed .is:

1. A coating composition consisting of (1) an aqueous dispersion resulting from .the polymerization in situ of vinylidene chloride polymer-forming monomers in a mixture consisting of water, an anionic dispersing agent, and catalytic amounts of ammonium pcrsulfate *and meta sodium .bisulfite, and (2) hydrogen peroxide'in an amount within the range of from about-0.1% to about 1% by weight, based onthe'tota'l weightof the dispersion.

'2. The coating composition of claim -1 wherein theamount of hydrogen peroxide is within the-range of' from about0.4% to about 05% by weight.

References Cited inathesfile of rthis patent UNITED STATES PATENTS 2,507,142 .Chaban May '9, 1950 2,570,478 Pitzl .Oct. 9, 195.1 

1. A COATING COMPOSITION CONSISTING OF (1) AN AQUEOUS DISPERSION RESULTING FROM THE POLYMERIZATION IN SITU OF VINYLIDENE CHLORIDE POLYMER-FORMING MONOMERS IN A MIXTURE CONSISTING OF WATER, AN ANIONIC DISPERSING AGENT, AND CATALYTIC AMOUNTS OF AMMONIUM PERSULFATE AND META SODIUM BISULFITE, AND (2) HYDROGEN PEROXIDE IN AN AMOUNT WITHIN THE RANGE OF FROM ABOUT 0.1% TO ABOUT 1% BY WEIGHT, BASED ON THE TOTAL OF THE DISPERSION. 